usermin mail problem

Virtualmin Theme version: 6.8
Virtualmin version: 3.67
Operating system: Redhat Enterprise Linux 5
my client complains that the junk email function always shows:
"An error occurred listing mail in this folder : Failed to login to POP3 server : Mailbox doesn't exist: Junk " .

How can I solve this problem?

Status: 
Closed (fixed)